This invention relates to storage tanks for food products in which hygienic conditions must be maintained, and is more particularly concerned with an agitator having an impeller blade that can be removed and replaced, and which is configured to be cleaned in place.
Storage tanks for processing of liquid food products, such as milk, dairy products, and fruit juices, can be provided in a variety of sizes and shapes, including silo tanks, which are elongated vertically, and horizontal tanks. In order to facilitate the cleaning of the interior of these tanks after a batch of the liquid food product has been drained, a number of clean-in-place techniques have been proposed, both for efficiency and for employee safety. Clean-in-place arrangements typically include one or more upwardly directed spray nozzles with associated tubing permanently installed in the interior of the tank. A cleaning fluid is applied to this system and the fluid sprays against the interior surfaces of the tank to clean any residues off. One clean-in-place arrangement is discussed in my prior U.S. Pat. No. 4,192,332.
For many liquid food product applications, an agitator is installed in the tank, with a shaft that penetrates a seal in the tank wall and an impeller blade or blades supported on the interior end of the drive shaft. Because food process standards do not permit any threaded fasteners to be exposed to the food product, the impeller is typically welded in place onto the end of the shaft. The clean-in-place nozzle can be directed towards the impeller for cleaning purposes, but it can only spray onto the front or distal side of the impeller. Accordingly, clean-in-place agitator arrangements have been proposed that permit the cleaning fluid to be fed under pressure into the shaft housing around the drive shaft. A mechanism such as a spray nozzle on the agitator shaft housing then directs a spray of the cleaning fluid at the proximal side of the impeller. Clean-in-place agitator assemblies have been proposed in U.S. Pat. No. 4,511,255 (Saucier), U.S. Pat. No. 4,168,918 (de Jonge), and U.S. Pat. No. 4,861,044 (Jay). Each of these requires some special configuration of the drive shaft, either so that it can be moved axially to carry out cleaning, that it have spray nozzles installed directly on the drive shaft, or that the drive shaft be provided with an annular flange of greater diameter than the remainder of the shaft.
In addition, the impellers or blades used on agitators of the prior art are welded in place on the tip of the shaft, and cannot be removed except by cutting them off. The need for precision welding makes it more expensive to install the agitator in the tank in the first instance, and also makes it difficult or impossible to reconfigure the agitator for different types of liquid food products. It is sometimes desirable to remove the drive shaft from the drive shaft housing, but because of the welded blade, or other structure present on the drive shaft as mentioned above, it is possible only to remove the drive shaft by pulling it into the interior of the tank, and in many cases it is not possible even to do this without removing the entire shaft housing from the tank. The agitator arrangements of the prior art do not permit removal and replacement of the drive shaft from the exterior, i.e., motor end of the shaft.